Fixed table containing only header generating broken markdown

[kaiser-chris]

There was a line break missing when generating a table with only the header row.
This fixes this problem.

[codecov]

Codecov Report

❗ No coverage uploaded for pull request base (dev@3b9e0ea). Click here to learn what that means.
The diff coverage is 100%.

@@          Coverage Diff          @@
##             dev     #10   +/-   ##
=====================================
  Coverage       ?   69.6%           
  Complexity     ?     184           
=====================================
  Files          ?      31           
  Lines          ?     612           
  Branches       ?      46           
=====================================
  Hits           ?     426           
  Misses         ?     167           
  Partials       ?      19

Impacted Files	Coverage Δ	Complexity Δ
.../net/steppschuh/markdowngenerator/table/Table.java	72.79% <100%> (ø)	28 <0> (?)

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[Steppschuh]

Good catch, thanks your contribution!